1. Field of the Invention
The present invention relates to a novel resin composition for electrodeposition paint and, in more detail, relates to a resin composition for electrodeposition paint capable of forming a coating film excellent in anticorrosivity and further excellent in low temperature curability.
2. Description of the Prior Art
As an electrodeposition paint is excellent in throwing power and capable of forming a coating film excellent in performances such as durability, anticorrosivity etc., it has been widely adopted conventionally in application fields where these performances are required, for example, coating of motorcar body, coating of electric appliances etc.
An electrodeposition paint generally consists of a resin containing hydroxyl group as a base resin and a polyisocyanate compound blocked with a blocking agent as a curing agent.
Conventional blocked polyisocyanates dissociate the blocking agent usually at a higher temperature than 160.degree. C., due to the structure of their blocking agent, and the freed isocyanate groups react with the hydroxyl groups of the base resin.
However, in recent years, plastics parts have been used together in case of coating of metal plates for car body in automobile industry and therefore a development of such a blocked polyisocyanate compound that dissociates the blocking agent at a low baking temperature, at which said plastics parts do not melt, and can react with the base resin.
As a method to dissociate the blocking agent from a blocked polyisocyanate compound at a relatively low baking temperature, for example, a process to block a polyisocyanate compound with an oxime has been known. However, there is a problem that an electrodeposition paint composition containing a polyisocyanate compound blocked with an oxime dissociates oxime blocking agent during storage, increases the paint viscosity and the smoothness of the electrodeposition coating surface deteriorates to a great extent.
The present inventors have been intensively conducting research aiming at developing a composition for electrodeposition paint, capable of solving problems such as mentioned above, excellent in storage stability and capable of forming a coating film excellent in low temperature curability. As a result, this time, they found that the above-mentioned purpose could be achieved by a resin composition for electrodeposition paint consisting of a resin containing hydroxyl group and a polyisocyanate compound blocked with an amidoalcohol having amide bond and alcoholic hydroxyl group in the molecule and completed the present invention.